1. Field of the invention
The present invention relates to a stirring device for mixing, drying, granulating or the like, and more particularly to a stirring device of the above type having a rotary drive shaft disposed inside a casing forming a stirring chamber and a plurality of paddles are fitted on the rotary shaft axially thereof.
2. Description of the prior art
According to a conventional stirring device of the above-noted type, the entire periphery of the interior casing surface facing the leading edge of the paddle is formed flat and smooth.
However, as is often the case with a stirring/mixing process of e.g. polyether and water-soluble polymer powder, with such a flat and smooth interior surface, there tends to occur adhesion of the processed substance to the operating paddle. The adhered substance grdually accumulates and hardens on the paddle and such accumulation causes a sliding action, i.e. frictional contact with the interior casing surface with each rotation of a paddle. Moreover, if the paddle keeps rotating with such viscous process-object substance adhered thereto, this means that there occurs constant mutual movement between the adhered substance and the paddle. In other words, the material is not fed from the inlet toward the outlet, but merely churned. These phenomena cause the troubles at specified below:
(a) As the repeated sliding contacts wear out the interior surface, the casing will be damaged quickly. Also, the fallout material of the worn-out surface will mix into the processed substance thereby deteriorating its quality.
(b) The paddle per se will also be damaged quickly from the mutual movement with the adhered substance.
(c) The paddle will be physically deformed due to a bending moment constantly applied thereto.
(d) There will occur significant power loss in the paddle rotation.
(e) The frictional contacts will cause considerably vibrations and noises.
Further, when a stirring process is carried out by the conventional device on a mixture of a water liquid containing water or additive added to a granule substance, the same troubles as noted above will occur.